1. Field of the Invention
The present invention relates to a ball valve having a valve seat sealing device, and particularly to a ball valve having a seat sealing device operated by a magnetic force for selectively compressing the valve seat against the valve ball, so that not only the leak-tight sealing effect can be greatly improved but also the wear between the valve ball and seat and the operative torque required for rotating the valve can be reduced.
2. Description of Related Art
A valve seat is a component of a ball valve. When the ball valve in a closed condition, contact surfaces are required to create between a valve ball and a valve body, so as to develop a sealing effect for preventing fluid leakage. In the past, a conventional ball valve, in order to achieve the sealing effect, normally applied soft material with resilience, such as Teflon or the like, to manufacture the valve seat for providing sealing surfaces between the valve seat and valve ball. Such soft material, however, will be deformed and distorted under a high-temperature and high-pressure condition, and therefore cannot provide a good sealing effect required for use in a high-temperature and high-pressure environment. U.S. Pat. Nos. 4,911,407 and 4,928,921 therefore provide a valve seat made from metallic material.
It is, however, difficult to manufacture a metal valve seat that can maintain good sealing effect, because of the high hardness and rigidity of metallic materal. In U.S. Pat. Nos. 4,911,407 and 4,928,921, metallic material with flexibility is applied to develop the leak-tight sealing effect between the valve seat and valve ball. Such a technology, however, is required a relatively high level of manufacturing technology that makes the cost for manufacturing increase greatly. Besides, in operating a ball valve having such kind of metal valve seat with flexibility, since the valve ball always tightly compresses against the valve seat, an increased friction force is created between the valve ball and the valve seat, such that an operative torque required for rotating the valve ball is greatly increased, and wear between the valve ball and the valve seat is also increased, which significantly reduces the life of the ball valve. In U.S. Pat. No. 4,968,000, springs are applied to associate with a metal valve seat to allow the valve seat to slide within the ball valve. U.S. Pat. No. 5,140,150 combines the technology of the flexible valve seat with the slidable valve seat. Since the resilience of a spring will deteriorate under high temperature, such a technology of using springs is not reliable in providing a ball valve to be used under high temperature environment.
Accordingly, an object of the present invention is to provide a ball valve having a magnetic seat sealing device that applies a magnetic mechanism to control a valve seat for selectively compressing against a valve ball, so that when the ball valve is in a closed condition, the magnetic mechanism exerts a magnetic force to the metal valve seat for further tightly compressing against the valve ball; and when the ball valve is in an open condition, the magnetic force is released to allow the valve seat to return its original position. In this way, the operative torque required for rotating the valve ball is significantly minimized, while maintaining the optimal sealing effect between the valve ball and the seat.
Additional objects, advantages, construction, and features of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings.